Interplay of cavity thickness and metal absorption in thin-film InGaN photonic crystal light-emitting diodes

Elizabeth Rangel,Evelyn L Hu,James S Speck,Yong-Seok Choi,Elison Matioli,Claude Weisbuch,Hung-Tse Chen

doi:10.1063/1.3480421

Abstract

Thin-film InGaN photonic crystal (PhC) light-emitting diodes (LEDs) with a total semiconductor thickness of either 800 nm or 3.45 μm were fabricated and characterized. Increased directional radiance relative to Lambertian emission was observed for both cases. The 800-nm-thick PhC LEDs yielded only a slight improvement in total light output over the 3.45-μm-thick PhC LEDs. Simulations indicate that, except for ultrathin devices well below 800 nm, the balance between PhC extraction and metal absorption at the backside mirror results in modal extraction efficiencies that are almost independent of device thickness, but highly dependent on mirror reflectivity.

Highlights

While the epitaxial thickness of conventional InGaN LEDs on sapphire is generally fixed by growth constraints to several microns or more, thin-film LEDs offer greater flexibility since the n-GaN can be thinned down after removal of the sapphire substrate
The thin PhC LEDs exhibited only a small improvement in total output power over the thick PhC LEDs. This result is explained by simulated extraction and absorption lengths for low-order modes, which indicate that the balance between extraction and absorption is maintained as the structure is thinned to 800 nm, resulting in an extraction efficiency that is largely independent of device thickness
061118-3 Rangel et al FIG. 4. ͑Color onlinea Simulated modal extraction efficiency for the TE0 and TE1 modes as a function of the total PhC LED thickness. ͑b Simulated modal extraction efficiency for the TE0 and TE1 modes in an 800-nm-thick PhC LED as a function of the mirror reflectivity

Summary

Introduction

We report on an experimental comparison between thin800 nmand thick3.45 ␮mvertically injected thin-film InGaN PhC LEDs. Despite a large difference in the number of guided modes supported by the two structures, the wavelength-integrated far-field patterns were reaElectronic mail: rangel@engineering.ucsb.edu. As shown in Fig. 3͑b, the thin PhC LEDs yielded an average enhancement over the unpatterned LEDs of 4.5 times—much higher than the enhancement in total power1.9 times—as a result of the vertical directionality of the PhC emission.

Results

Conclusion